Posted
by
samzenpuson Thursday April 19, 2012 @01:33AM
from the break-it-down dept.

ananyo writes "Condensed-matter physicists have managed to detect the third constituent of an electron — its 'orbiton'. Isolated electrons cannot be split into smaller components, earning them the designation of a fundamental particle. But in the 1980s, physicists predicted that electrons in a one-dimensional chain of atoms could be split into three quasiparticles: a 'holon' carrying the electron's charge, a 'spinon' carrying its spin and an 'orbiton' carrying its orbital location. In 1996, physicists split an electron into a holon and spinon. Now, van den Brink and his colleagues have broken an electron into an orbiton and a spinon (abstract). Orbitons could also aid the quest to build a quantum computer — one stumbling block has been that quantum effects are typically destroyed before calculations can be performed. But as orbital transitions are extremely fast, encoding information in orbitons could be one way to overcome that hurdle."

Wikipedia says this about Mott insulators: Mott insulators are a class of materials that should conduct electricity under conventional band theories, but are insulators when measured (particularly at low temperatures). This effect is due to electron-electron interactions which are not considered in conventional band theory.

The article is talking about quasiparticles, that is, collective excitations in some medium that behave as though they were individual particles. Think about a Newton's cradle (that thingy with the balls that click back and forth). When a ball hits one end of the device, a ball emerges from the other end of the device. It's as though there were some kind of particle (there's a mandatory rule that we have to give it a stupid name, so let's call it a ballon) that is transmitted through the device. Now, even though we know that there's no actual particle traveling through the device, we can make calculations as though there were, and this makes things simpler to work with.

Condensed matter physicists work with much more complicated media and their particles are quantum rather than classical, but otherwise the idea is the same. In this case, they have a medium consisting of a strontium cuprate wire, which, of course has lots of electrons in its atoms. They fire a beam at it (like the ball hitting the Newton's cradle) and this excites stuff in the wire, which they find acts like quasiparticles of a particular kind.

The exact kind of quasiparticle is one that acts like an electron, but has no charge or spin, just orbital properties. The spin and charge kinds of quasiparticle were previously discovered, and this completes the set, which is why it's news.

I believe you're over-thinking the one-dimensional attribute. It simply means they're using a straight-line chain of the molecules in question. There are no molecules in the construct branching off at any other angle, that's all.

There are not that many, and there isn't a good systematic way to name them anyway. The root of the word denotes the basic property that describes the particle.

'holon' comes from 'hole', which is the absence of a particle. that may sound weird, but in quantum mechanics, everything is discrete so a particle present or absent is like a binary 1 or 0, and the 0 states (holes) are just as good as 1 states (particles).

'spinon' comes from 'spin', which is the intrinsic angular momentum.

'orbiton' comes from 'orbital', which is the agular momentum from the orbital motition around the nuclei.

There are lots of other quasi-particles that occur in condensed matter, pasmons, phonons, polarons, polaritons, and so on. They all arise as emergent effects from interactions between large numbers of 'fundamental' particles, such as electrons.

The article is talking about quasiparticles, that is, collective excitations in some medium that behave as though they were individual particles. Think about a Newton's cradle (that thingy with the balls that click back and forth). When a ball hits one end of the device, a ball emerges from the other end of the device. It's as though there were some kind of particle (there's a mandatory rule that we have to give it a stupid name, so let's call it a ballon) that is transmitted through the device. Now, even though we know that there's no actual particle traveling through the device, we can make calculations as though there were, and this makes things simpler to work with.

Condensed matter physicists work with much more complicated media and their particles are quantum rather than classical, but otherwise the idea is the same. In this case, they have a medium consisting of a strontium cuprate wire, which, of course has lots of electrons in its atoms. They fire a beam at it (like the ball hitting the Newton's cradle) and this excites stuff in the wire, which they find acts like quasiparticles of a particular kind.

The exact kind of quasiparticle is one that acts like an electron, but has no charge or spin, just orbital properties. The spin and charge kinds of quasiparticle were previously discovered, and this completes the set, which is why it's news.

More specifically, "separation" refers to the prediction (and now observation) that in the collection of electrons in the 1D wire, orbital, spin, and charge information travel at different speed. This is in particular a low dimensional effect. Hence this is observed in a quantum wire.

Unfortunatly, they didn't select my submission [slashdot.org], but the idea is basically unbound electrons have some quantum numbers related to spin and charge, but electrons bound to a nucleus have another quantum property related to the orbital they exist in (as a result of all those pesky electron orbital exclusion properties we get a taste of in chemistry 101). This gives the electron a sort of angular momentum quantum property (that is angular momentum isn't a continuous property, but is quantized to certain discrete values).

You might imagine that in the classical sense, if you bumped an electron out of orbiting one nucleus and it be bound to the next nucleus in a lattice, the idea of what angular momentum all the electrons had would be somehow be conserved as a whole in the system on average. Now you toss in the fact that in a lattice, these otherwize local effects of virtually exchanging angular momentum might become delocalized from their actual particles and still maintain the required system average and also (in certain circumstance) still reveal their orignal quantum nature (instead of continuous approximation), that's the effect you have. It isn't a real particle exhibiting quantum effects, but a quasi-particle, but in some sense we've split-off the angular momentum effect from the actual electron that is bound (w/o unbinding the electron).

If you are familiar with semiconductors, you can often hear of people talking about "holes" conducting electric charge like they are electrons, but they aren't electrons: it's a "hole" in a sea of delocalized electrons doing that charge transport. Usually the effects we are interested in are quite classical (say like average current), but in smaller dimensions and lower energy levels we start exhibiting quantum effects of these quasi-particles (say like in supercondutors).

I don't know how this orbiton angular momentum thing will be useable. The effect that was observed was that excitation to higher orbits (higher angular momentums), can propagate in the lattice which seems less useful (eventually you are in such a high excitation energy, you are beyond most interesting quantum effects or effectively unbound). One speculation that I have is that certain insulator properties will be quantized (if certain orbits are unavailable, and the incoming quantum angular momentum is incompatible with the available orbits), and maybe that can be used for some storage capabiltiy or maybe somehow helping spintronics (which is sort of what these folks were thinking).

The original names for quarks were based upon a poem by James Joyce [wikipedia.org]. There are some other rather esoteric names that have come up in science over the years so such references really aren't totally unheard of.